MOCVD system for forming superconducting thin films

Abstract

A system for MOCVD fabrication of superconducting oxide thin films provides a feed tube having a narrow slot along its length with a uniform mixture of powdered precursor materials packed inside the tube. The mixture composition is such that the resulting film has the desired stoichiometry. The tube moves downward at a controlled rate past a bank of heating lamps surrounded by a heat reflector. At each position of the tube this structure heats a localized section of the precursor material, with a sharp temperature gradient at the boundary of the section so that the heating is confined to this section. The precursor material in the heated section is substantially completely vaporized, with negligible decomposition and nonvolatile residue formation, and the vaporization rate is governed by the downward velocity of the tube. The vaporized material escapes through the longitudinal slot, and is swept by a carrier gas into a reaction zone. Oxygen is mixed with the gas stream, and the reaction products are deposited as a thin film on the substrate. A modification of this system includes coils adjacent to the reaction zone, connected to an rf generator. These coils produce a plasma in the reagent gas mixture that enhances the chemical reaction.

What is claimed is: 
     
       1. Apparatus for metalorganic chemical vapor deposition of thin films, comprising: (a) an elongated feed member containing a uniform mixture of precursor materials distributed along the length of said member, said mixture having a composition such that said films have the desired stoichiometric ratios of elements, said mixture being contained such that upon heating a localized section of said member above the vaporization temperatures of said precursor materials the vaporized precursor materials can escape from said feed member in a direction perpendicular to the longitudinal axis of said member;   (b) heating means for raising the temperature of a localized section of said elongated feed member above the vaporization temperatures of said precursor materials, and for vaporizing substantially all of said precursor materials in said section, such that at the boundary between said localized section and the unvaporized precursor materials outside of said section the temperature gradient has a large magnitude along the longitudinal direction;   (c) drive means for continuously varying the localized section of said elongated feed member that is heated by said heating means;   (d) transport means for transporting said vaporized precursor materials from said elongated feed member to a reaction zone where said vaporized precursor materials undergo the desired chemical reaction; and   (e) a substrate located in said reaction zone such that the products of said chemical reaction are deposited on said substrate and form said thin film.   
     
     
       2. Apparatus according to claim 1, wherein said elongated feed member comprises a tube having a longitudinal slot through the tube wall parallel to the axis of the tube, and wherein said mixture of precursor materials is contained inside said tube. 
     
     
       3. Apparatus according to claim 1, wherein said elongated feed member is oriented such that nonvolatile decomposition products formed in said localized section by the heating of precursor materials in said section flow away from said unvaporized precursor materials outside of said section. 
     
     
       4. Apparatus according to claim 3, wherein said elongated feed member comprises a tube having a longitudinal slot through the tube wall parallel to the axis of the tube, and wherein said mixture of precursor materials is contained inside said tube. 
     
     
       5. Apparatus according to claim 4, wherein said tube is oriented such that one end of said tube is substantially lower than the opposite end of said tube, and wherein the location of the localized section of said tube whose temperature is raised by said heating means is varied continuously by said drive means along said tube in the direction of increasing elevation. 
     
     
       6. Apparatus according to claim 5, wherein said tube is oriented with its axis in the vertical direction. 
     
     
       7. Apparatus according to claim 5, wherein said heating means comprises fixed heating means for heating the material in a fixed region of space such that said tube extends downwardly into said fixed region, and wherein said drive means comprises (a) a support member rigidly attached to said tube; and   (b) a drive mechanism connected to said support member such that said drive mechanism moves said support member continuously along a path parallel to the longitudinal axis of said tube in the direction of decreasing elevation.   
     
     
       8. Apparatus according to claim 7, wherein said tube is oriented with its axis in the vertical direction. 
     
     
       9. Apparatus according to claim 7, wherein said fixed heating means comprises (a) a heat radiator in spatial proximity with the localized section of said tube extending into said fixed region of space; and   (b) a heat reflector surrounding said fixed region of space and having openings at the locations where said tube intersects the boundaries of said fixed regions such that said tube extends through said openings into said fixed region of space.   
     
     
       10. Apparatus according to claim 1, wherein said transport means comprises (a) a carrier gas; and   (b) means for propelling said carrier gas, such that said carrier gas passes by said elongated feed member, entrains said vaporized precursor materials, and transports said precursor materials into said reaction zone.   
     
     
       11. Apparatus according to claim 10, further comprising oxygenation means for introducing oxygen into said carrier gas at a controlled rate prior to said carrier gas entering into said reaction zone. 
     
     
       12. Apparatus according to claim 1, further comprising means for heating said substrate. 
     
     
       13. Apparatus according to claim 1, further comprising means for producing a plasma in said vaporized precursor materials in said reaction zone. 
     
     
       14. Apparatus according to claim 11, further comprising means for producing a plasma in said carrier gas into which oxygen and vaporized precursor materials have been introduced in said reaction zone. 
     
     
       15. Apparatus for metalorganic chemical vapor deposition of thin films, comprising: (a) an elongated feed member containing a plurality of precursor mixtures distributed along the length of said member, such that each of said precursor mixtures is a uniform mixture of precursor materials having a composition such that the resulting film layer formed from said precursor mixture has the desired stoichiometric ratio of elements, wherein each of said precursor mixtures is contained in a corresponding precursor section along the length of said member, and such that upon heating a localized portion of said precursor section above the vaporization temperatures of the precursor materials in said section, the vaporized precursor materials in said section, the vaporized precursor materials can escape from said feed member in a direction perpendicular to the longitudinal axis of said member;   (b) heating means for raising the temperature of any localized portion of any precursor section above the vaporization temperatures of said precursor materials, and for vaporizing substantially all of said precursor materials in said portion, such that at the boundary between said localized portion and unvaporized precursor materials outside of said portion the temperature gradient has a large magnitude along the longitudinal direction;   (c) drive means for continuously varying the localized portion of said elongated feed member that is heated by said heating means;   (d) transport means for transporting said vaporized precursor materials from said elongated feed member to a reaction zone where said vaporized precursor materials undergo the desired chemical reaction; and   (e) a substrate located in said reaction zone such that the products of said chemical reaction are deposited on said substrate and form said thin film.   
     
     
       16. Apparatus according to claim 15, wherein said precursor sections are disposed along the length of said feed member such that each pair of adjacent precursor sections is separated by a spacer section, and further wherein each spacer section does not contain any material that can affect the chemical vapor deposition of the precursor materials. 
     
     
       17. Apparatus according to claim 15, wherein said elongated feed member comprises a tube having a longitudinal slot through the tube wall parallel to the axis of the tube, and wherein said mixtures of precursor materials are contained inside said tube. 
     
     
       18. Apparatus according to claim 15, wherein said elongated feed member is oriented such that nonvolatile decomposition products formed in said localized section by the heating of precursor materials in said section flow away from said unvaporized precursor materials outside of said section. 
     
     
       19. Apparatus according to claim 18, wherein said elongated feed member comprises a tube having a longitudinal slot through the tube wall parallel to the axis of the tube, and wherein said mixtures of precursor materials are contained inside said tube. 
     
     
       20. Apparatus according to claim 19, wherein said tube is oriented such that one end of said tube is substantially lower than the opposite end of said tube, and wherein the location of the localized portion of said tube whose temperature is raised by heating means is varied continuously by said drive means along said tube in the direction of increasing elevation. 
     
     
       21. Apparatus according to claim 20, wherein said tube is oriented with its axis in the vertical direction. 
     
     
       22. Apparatus according to claim 20, wherein said heating means comprises fixed heating means for heating the material in a fixed region of space such that said tube extends downwardly into said fixed region, and wherein said drive means comprises (a) a support member rigidly attached to said tube; and   (b) a drive mechanism connected to said support member such that said drive mechanism moves said support member continuously along a path parallel to the longitudinal axis of said tube in the direction of decreasing elevation.   
     
     
       23. Apparatus according claim 22, wherein said tube is oriented with its axis in the vertical direction. 
     
     
       24. Apparatus according to claim 22, wherein said fixed heating means comprises (a) a heat radiator in spatial proximity with the localized section of said tube extending into said fixed region of space; and   (b) a heat reflector surrounding said fixed region of space and having openings at the locations where said tube intersects the boundaries of said fixed regions such that said tube extends through said openings into said fixed region of space.   
     
     
       25. Apparatus according to claim 15, wherein said transport means comprises (a) a carrier gas; and   (b) means for propelling said carrier gas, such that said carrier gas passes by said elongated feed member, entrains said vaporized precursor materials, and transports said precursor materials into said reaction zone.   
     
     
       26. Apparatus according to claim 25, further comprising oxygenation means for introducing oxygen into said carrier gas at a controlled rate prior to said carrier gas entering into said reaction zone. 
     
     
       27. Apparatus according to claim 15, further comprising means for heating said substrate. 
     
     
       28. Apparatus according to claim 15, further comprising means for producing a plasma in said vaporized precursor materials in said reaction zone. 
     
     
       29. Apparatus according to claim 26, further comprising means for producing a plasma in said carrier gas into which oxygen and vaporized precursor materials have been introduced in said reaction zone.